His first point is that knowledge about economic development is very limited. Much of economic growth has to be attributed to the "residual" -- "the measure of our ignorance," as Robert Solow calls it. In the best studied case, the United States, two-thirds of the rise in per capita income falls within this category. Similarly, the Asian NICs provide "no obvious lessons," having followed "varied and ambiguous" paths that surely do not conform to what "current orthodoxy says are the key to growth." Krugman recommends "humility" in the face of the limits of understanding, and caution about "sweeping generalizations.&quot.